Several steered and so-called radial trucks have been developed utilizing various means of inducing the wheels and axles of a railroad freight car truck or passenger truck to assume a radial position when entering and negotiating curved track and of controlling the lateral stability of the wheelsets at high speeds on straight (tangent) track. All required major changes from the conventional side frame and bolster, and most failed to provide the necessary high speed tracking (or hunting) control. In addition, the steering means in most cases prevented observation of some vital parts of the truck, such as the brake shoes, and interfered physically with the servicing of these important components.
A further problem with prior art steering arm construction was in the considerable difficulty of assembly and disassembly of either the truck parts, steering components or both, to the extent that the concept has faced much resistance from the industry.
The List radial truck construction as shown in U.S. Pat. No. 3,789,770 and modified, has been proved by tests to be capable of providing the slow speed curving ability and high speed stability desired.
A major consideration is that the standard railroad truck has been many years in the development and proved to be a very reliable unit for the very severe environment that constitutes general railroad operation, and much technical background, testing and fatigue evaluation has been developed. The instabilities and poor curving symptoms that currently plague the unit were brought about by relatively recent increases in operating speeds and car size, high mileage, the elimination of spring planks and on the high capacity cars, the adoption of roller bearings which do not provide the freedom to accommodate the lateral deviations of the car or track, and consequently transmit the disturbances to the truck to initiate periodic oscillations of vibration called hunting.
To completely change the basic three-piece truck obviously would be a major step both from the technical and economic standpoint and probably prohibitive for the industry.
Accordingly, the primary object of the instant invention is to provide a steering arm construction that can be retrofitted to the standard truck to provide the proven advantages of radial steering and high speed lateral control without the necessity of making changes to the side frames or bolster.
A further object is to provide steering equipment that does not interfere with the foundation brake rigging, obscure the brake shoes from inspection, or complicate the brake maintenance procedures.
A still further object is to provide steering arms compatible with the conventional truck in that the assembly and disassembly of the truck components is not hampered.
Another object is to provide the steering function using a simple steering arm construction that, fail safe in the event of a mishap, i.e., will not negate the basic three-piece truck integrity.
Still another object is to provide steering arms that will allow ample flexibility of the truck to negotiate spiral track and maximum warped track without restriction.
Yet another object is to provide steering arms that utilize the existing space envelope within the conventional truck side frame and bolster assembly.